[sailfrog]

"But HFT looks to me like they're just sucking little pieces out of everyone else's trades, while providing no value to society."

This suggests that market participants of any type provide "value to society". Their is only one reason any entity participates in the market, and it has nothing to do altruism, and everything to do with making money for themselves or their clients. Capitol allocation to companies going public is over once the shares are issued via the IPO auction. No transaction on the secondary market results in any money going back to the company that issued the shares. So how does the length of time a firm holds onto a stock before attempting to realize profits define whether or not they provide value?